Microwave components and systems are of immense importance for commercial and defense applications. Thin film technology has become integral for the fabrication of microwave components and systems. Due to continuously increasing microwave frequencies with decreased feature sizes, thin film technology has found wide spread applications.
Thin film microwave circuits require substrates which have very low dielectric loss at microwave frequencies. Dielectric materials having high dielectric constant and low dielectric loss at microwave frequencies are required to minimize losses in the microwave systems. Substrate properties, such as surface finish, and the fabrication processes, such as metallization and definition, determine the microwave circuit performance.
For optimum performance, the microwave substrate requires low loss tangent to reduce dielectric loss. The microwave substrate also requires that the dielectric constant remain stable during the batch manufacturing process. Additionally, the substrate requires a smooth surface finish to minimize conductor Ohmic losses; high chemical resistance; and stable temperature and frequency of the dielectric properties.
Thin films of dielectric materials having high dielectric constant, low dielectric loss, and good temperature and frequency stability are attractive for high frequency microwave applications.
Thin film processing technology allows fabrication of small conductive and resistive patterns for high frequency applications. Thin films of dielectric materials also offer a great variety of applications in semiconductor device technology, including but not limited to etching masks, barrier layers, gate oxide, separation of active and passive components, and electrical isolation between conductive regions.
Thin films of high dielectric constant materials have attracted considerable attention for their potential applications in dynamic random access memory devices. Although many materials possess high dielectric constants which are capable of substantially increasing capacitance, thin film technology has not been benefited. This is because materials capable of high dielectric constants are often plagued with poor leakage characteristics, incompatible for manufacturing purposes, unable to extend for multiple generations, unstable for subsequent processing, i.e. multiple metallization layers, substantially impact on existing complimentary metal-oxide-semiconductor (CMOS) structures, and do not provide optimal design characteristics to allow for proper temperature and bias stability.
Due to its high dielectric constant low leakage current, low defect density and high breakdown field strength, Ta2O5 is a promising material for thin film applications. Ta2O5 has particular applicability in high density dynamic random access memories (DRAMSs), integrated capacitor, electroluminescent display devices, and gate dielectrics of metal-oxide-semiconductor (MOS) devices ( see M. Anthony et al, TI Technical Journal 12, 30 (1995)).
Ta2O5 is a suitable alternative to conventional insulator materials like Si3N4 and SiO2 in VLSI technology. The high dielectric constant and low loss insulating materials are also attractive for microwave devices. For successful integration into these electronic devices, extremely reliable Ta2O5 films with high, temperature and field stability are desired.
Recently, there has been interest in Ta2O5 based composite insulator because of the improved electrical properties compared to other insulating materials. It has been shown that the electrical properties of bulk Ta2O5 can be significantly improved through substitution of Al2O3 and TiO2 (see R. J. Cava et al, Nature 377, 215 (1995) and Appl. Phys. Lett. 70, 1396 (1997)).
For microelectronic applications good quality thin films of these composite materials with enhanced electrical properties, meeting the requirements of integrated electronic devices, are required.